Electrocoating feed control process and apparatus



Feb. 21, 1967 [GRAS T 3,305,467

ELECTROCOATING FEED CONTROL PROCESS AND APPARATUS 4 Sheets-Sheet 1 Filed July 1,. 1965 v. Q A L .m \N m mm WN I. A u T A \fl j W \M k mmm m? T 0G 6 Q 6 HEHHR mlw 3'; RAYMOND A. J's/ms 60/?00 6. STAOSBERG INVENTORS HTTOR/VEVS Feb. 21, 1967 ELECTROCOATING FEED CONTROL PROCESS AND APPARATUS Filed July 1, 1963 F/& 2

4 Sheets-Sheet 2 RAYMOND A [GR/1.5

GORDON 6. 5 TROSfif/QG INVENTORS -Feb. 21, 1967 R. A. IGRAS ETAL ELECTROCOATING FEED CONTROL PROCESS AND APPARATUS Filed July 1, 1963 4 Sheets-Sheet 4 RAYMOND 4. [UR/45 6020 0/\/ c; smasafiea INVENTORS BYWfW United States Patent M 3,305,467 ELECTROCOATING FEED CQNTROL PROCESS AND APPARATUS Raymond A. Igras, Dear-born Township, Wayne County, and Gordon G. Strosherg, Oak Park, Mich, assignors to The Ford Motor Company, Dearborn, Mich, a corporation of Delaware Filed July 1, 1963, Ser. No. 291,624 8 Claims. (Cl. 204181) Thi invention relates to electrocoating electrically conductive objects with an organic coating material dispersed in an aqueous bath. In particular, this invention relates to a method for controlling product quality and improving the efliciency in a continuous, or intermittently continuous process of anodic deposition wherein organic film-forming material is thus deposited upon a conductive substrate within an aqueous bath so as to form a substantially Water insoluble coating thereon. More particularly, this invention relates to the use of a novel feed control system in combination with an electrocoating process whereby electric-a1 connection with adjacent and individually suspended workpieces is automatically measured and entry of such objects into the bath prevented when the current flow therebetween exceeds a predetermined value.

Objects to be coated are individually suspended from and transported by an overhead conveyor which, with suitable connecting devices, is constructed and arranged such that the suspended workpieces successively enter the aqueous bath for coating and are withdrawn for further processing such as sanding, finish coating, etc.

While the object is being coated the workpiece is positively charged and a direct current flow of electrical energy is provided between the workpiece and a negative and grounded coating tank or other electrode. However, it has been found advantageous in many embodiments of electrocoating to reverse the polarity of the workpiece upon entering or leaving the bath and/or during submergence in the bath. Under such conditions electrical connection between adjacent workpieces prevents maintenance of a constant coating time or renders at least a portion of such coating time substantially ineffective. Improperly positioned objects on the conveyor line, overlapping extensions, misplaced extraneous objects and a variety of other causes can bring about the closing of an electrical circuit between adjacent objects.

In accordance with this invention the resistance to flow of electrical energy between each workpiece and the workpiece immediately following or the next succeeding hanger if empty is automatically measured as the workpiece approaches the electrocoating bath. If the resistance of such insulation to the flow of electrical energy is found to be below a predetermined value, a warning system is automatically actuated and/or the conveyor is automatically halted until the electrical connection can be eliminated.

Organic coating materials which may be used in the bath include but not by way of limitation alkyd resins, acrylate resins, phenol-formaldehyde resins and various carboxylic acid resins or mixtures of the foregoing with each other or other film-forming materials including binding agents and extenders conventionally employed with water based paints. Such materials may include or be employed with other organic monomers and/ or polymers including but not by Way of limitation hydrocarbons and oxygen substituted hydrocarbons such as ethylene glycol, propylene glycol, glycerol, carbitol, methanol and various carboxylic acids, ethers, aldehydes and ketones. The filmforming material may include or be employed with pigments, dyes, drying oils, etc., and may be dispersed as a colloid, emulsion or emulsoid.

3,305,467 Patented Feb. 21, 1967 The organic coating material is dispersed in the bath with the aid of a conventional dispersing agent. These include water soluble ammonium and basic amine salts, polymeric amines, etc. Such materials are described at length in US. Patent 2,530,366 to A. G. Gray and elsewhere in the literature.

It is one object of this invention to improve product quality control and promote operational efficiency in an electrocoating process by providing method and means for accurately detecting the approach of two adjacent workpieces in electrical connection with each other and to prevent the same from entering the coating bath.

With the foregoing and other objects in view, as will hereinafter become apparent, this invention comprises the methods, combinations, construction and arrangement of parts hereinafter set forth, disclosed, claimed and illustrated in the accompanying drawings wherein:

FIGURE 1 is a schematic drawing depicting electrocoating apparatus with which the feed control systems shown in the succeeding figures are employed.

FIGURE 2 is a schematic drawing illustrating an automatic feed control system for use with the electrocoating apparatus of FIGURE 1, said system being adapted to measure the electrical resistance between uniformly suspended, adjacent workpieces; signal the approach of electrically connected workpieces; and stop the conveyor for elimination of such electrical connection.

FIGURE 3 is a schematic drawing illustrating an automatic feed control system similar to that shown in FIG- URE 2 but adapted for use with a mixed product line wherein workpieces requiring single and multiple suspensions are irregularly intermixed on the conveyor line.

FIGURE 4 is a schematic drawing illustrating the check and control device of FIGURES 2 and 3 whereby the resistance between adjacent workpieces is measured automatically as they approach the electrocoating bath.

Referring now to FIGURE 1, chemically resistant tank 11 contains a coating bath 13 and serves as a negative electrode in the coating process. Tank 11 is connected to DC. power source 59 via conductor 56. The articles to be coated 15 and 17 are placed upon conductor hangers 19 and 21, respectively, which in turn are suspended from and transported through bath 13 by a conveyor 23 which may be of the conventional chain driven variety. Hangers 19 and 21 include insulators 25 and 27 respectively which insulate articles 15 and 17 from the grounded conveyor. Contact plates or brushes 2.9 and 31 are attached to and in electrical connection with hangers 19 and 21 respectively. Contact plates 29 and 31 are shown approaching the bath and in electrical contact with check segments 24 and 26 of segmented bus bar 33. Segments 24 and 26 are separated from each other by insulator 32 and from the remainder of the bus bar 33 by insulators 30 and 34 respectively. In addition to check segments 24 and 26 bus bar 33 includes bath approach segment 35, a withdrawal segment 45, and a plurality of intermediate segments 37, 39, 41 and 43 here shown separated by insulators 36, 38, 42 and 44 respectively.

In this embodiment approach segment 35 is negative or of opposite polarity to the coating polarity of the workpiece. Segment 35 is here shown in electrical connection with DC. power source 59 through conductor 54. As article 15 approaches the bath a set of contacts indicated at 47 is closed and segment 37 is of the same polarity as approach segment 35. As article 15 moves from right to left with respect to the drawing, brush 29 which is of suflicient length to extend across insulator 36 passes over insulator 36 and contacts segment 37 while still in contact with segment 35. Article 15 is then in electrical contact with segment 37 via hanger 19 and brush 29. By this time article 15 has passed beneath the surface of bath 13 and brush 29 trips limit switch 49. This tripping of switch 49 opens the set of contacts indicated at 47 and closes the set of contacts indicated at 51 by electromechanical means or other suitable devices thereby breaking the electrical connection between segments 35 and 37 and establishing an electrical connection between segments 37 and 39.

The connecting mechanisms between limit switch 49 and contacts 47 and 51 are not shown in the drawing, but it will be understood by those skilled in the art that this action can be carried out in a variety of ways with conventional switching devices. For example, switch 49 may be arranged such that upon being mechanically tripped by the movement of brush 29 it will actuate a conventional electrical contact. This in turn will energize a conventional relay which will energize contactors which will force open the set of contacts indicated at 47 and close the set of contacts indicated at 51.

Segment 39 is positively charged being connected to conductor 53, a positive lead from D.C. power source 59. Therefore, the closing of the set of contacts indicated at 51 imparts positive polarity to article initiating the coating period or cycle when the set of contacts indicated at 61 on conductor 53 is closed. When the set of contacts indicated at 61 is open, as here shown, initiation of the coating period is delayed until the closing of the same imparts a positive polarity to segment 39 or until brush 29 comes into contact with a succeeding segment of bus bar 33 that is so charged. This provision for delay in initiating coating is to provide means for maintaining a constant coating time in the event that the speed of the conveyor line is reduced in accordance with reduced product schedules. Provision is made for actuation of segment 39, i.e., establishing electrical connection with power source 59, through limit switch 55. In this embodiment the tripping of limit switch 55 actuates a timing device, not shown, through which the closing of the set of contacts indicated at 61 is effected after a predetermined time by conventional switching devices. The tripping of limit switch 55 also serves to open the set of contacts indicated at 51 and close the contacts at 47 through mechanisms actuated in a manner either identical or similar to that described in connection with limit switch 49. This opening of the contacts at 51 and closing of contacts at 47 returns the approach mechanism to the original electrical condition and the article 17 can then be brought into bath 13 in the same manner as heretofore described for article 15.

In this embodiment segment 41 is shown connected to DC. power source 59 by conductor 57 which is equipped with a set of contacts indicated at 63. It is to be understood that segment 41 may be supplemented by any desired number of similar segments which in turn may be connected to power source 59 by leads equipped with contacts similar to those shown at 61 and 63. These contacts in turn may be connected with limit switches, timing devices, and/ or similar equipment as desired to regulate coating time automatically or otherwise in accordance with conveyor speed changes.

As article 15 proceeds through bath 13 brush 29 eventually contacts limit switch 65 which opens the set of contacts indicated at 67 and closes the set of contacts indicated at 69 through mechanisms actuated in a manner identical or similar to those aforedescribed in connection with limit switch 49. Segment 43 is thus placed into electrical connection with withdrawal segment 45. Conductor 58, a negative lead from DC. power source 59, provides electrical connection between segment 45 and source 59. Limit switch 65 is positioned on the line such that its actuation and the resulting opening of the set of contacts indicated at 67 will terminate the coating cycle while article 15 is still immersed to the desired depth in bath 13. In the continuation of the withdrawal movement brush 29 trips limit switch 71 which, through suitable mechanisms, not shown, opens the contacts at 69 and closes the contacts at 67 leaving the withdrawal system in the same electrical condition it assumed prior to the tripping of limit switch 65 by brush 29. Article 17 may then be brought through the withdrawal mechanism in an identical manner. A coating potential in the range of about 50 to 1000, preferably to 500, volts ordinarily will be found most satisfactory.

Tank 11 is equipped with one or more agitation means here represented by propeller 73 and means for rotating such propeller indicated by electric motor 75. Motor 75 is electrically connected by suitable conductors, not shown, to a suitable power source. This power source may be DC. power source 59 if a direct current motor is used, or it may be an independent source and the motor may be adapted for use with either alternating current or direct current.

In this embodiment a fixed auxiliary electrode 77 is shown immersed beneath the upper surface of bath 13. Electrode 77 is in electrical connection with tank 11 through conductors 76 and 78. This electrode is representative of one or more such electrodes which may be employed to facilitate the coating of the center portion of the top surface of a wide workpiece, e.g., the top of an automobile body.

Referring now to FIGURE 2, articles 15 and 17 are again shown suspended from conveyor 23 by hangers 19 and 21 and insulators 25 and 27 respectively with their respective bus bar contacts, brushes 29 and 31, in electrical contact with bus bar segments 24 and 26 respectively. Conveyor 23 is electrically driven by conventional power source, not shown, via conductors 131 and 133 and a conventional drive mechanism indicated generally at 135 which comprises electric motor 137, reducer 139, chain 141 and their conventional connections, not shown.

A check and control device indicated generally at 147 is adapted to automatically measure the resistance between adjacent workpieces, article 15 and article 17, and to signal the operator and stop the conveyor if such resistance is elow a predetermined value. The resistance measuring mechanism of device 147 is in electrical connection with segments 24 and 26 via conductors 143 and 145 respectively. This device is described hereinafter with FIGURE 4.

The resistance measuring mechanism of device 147 is electrically connected to an alternating current power source, not shown, by conductor 149, switch 151, and conductors 153 and 155. Relay coil 157 for activating a set of contacts indicated at 159 is in electrical connection with conductors 153 and 155. The contacts of thi set are closed when the conveyor is running and are in electrical connection with conductor 131 of the conveyor run circuit. Signal light 161 is in electrical connection with conductor 153 and with conductor when the set of contacts indicated at 163 is closed. A hell or other warning device maybe substituted for the signal light. The contacts of this set are normally open and are activated by relay coil 171 which also activates a set of contacts indicated at 173. The contacts of this set are normally closed and are in electrical connection with conductor 131 of the conveyor circuit. Coil 171 is in electrical connection with conductor 155 and with terminal 175 of device 147. Terminals 177 and 179 of devices 147 are here shown in electrical connection with conductors 181 and 183 which in turn are in electrical connection with a spring actuated pressure switch or reset button 185. The operation of switch 185 is described hereinafter with FIGURE 4.

Referring now to FIGURE 3, the portion of bus bar 33 here shown includes segments 24 and 26 and insulators 30, 32 and 34 shown in the previous figure. In addition, this view includes segments 20 and 22 and insulator 28. The resistance measuring mechanism of device 147 is the same as that shown in FIGURE 2 and here is in electrical connection with segment 26 via conductor 143 as in the previou figure and is elsewhere in electrical connection with bus bar 33 via conductor 245. Articles 2111, 208, and 218 are suspended from conveyor 23 by hangers 2112, 209, 210 and 219 as were the workpieces in the preceding figures with the exception that article 208 is supported by two separate hangers. Hangers 202, 209, 210 and 219 are each insulated from the grounded conveyor by insulators 2113, 211, 212 and 221 respectively and are in electrical connection with brushes 2114, 213, 214 and 222 all of which are in electrical contact with segmented bus bar 33. Hangers 2112, 209' and 219 are also equipped with movable dogs or tripping means 205, 215 and 223 respectively positioned and arranged to engage and trip movable arms 2116 and 216 of limit switches 257 and 217 respectively. Limit switches 207 and 217 are held in position by conveyor support means, not shown. Conveyor 23 is electrically driven as in the preceding figure by a conventional power source, not shown, via conductors 131 and 133 and a conventional drive mechanism indicated generally at 135 which comprises electric motor 137, reducer 13-9, chain 141, and their conventional connections, not shown.

A check and control device generally indicated at 147 is adapted to automatically measure the resistance between adjacent workpieces as their respective brushes move into electrical contact with sections 24 and 26 or 22 and 26 of segmented bus bar 33, and to signal the operator and stop the conveyor if such resistance is below a predetermined value.

Conductor 245 is provided with a set of contacts indicated at 225 which, when closed, provides electrical connection between device 147 and segment 24. Conductor 245 is also provided with a set of contacts indicated at 227 which when closed, as here shown, provides electrical connection between device 147 and segment 22. As in the previous figure, the resistance measuring mechanism of device 147 is electricailly connected to an alternating current power source, not shown, by conductor 149, switch 151, and conductors 153 and 155. Relay coil 157 for activating a set of contacts indicated at 159 is in electrical connection with conductors 153 and 155. The contacts of this set are closed when the conveyor is running and are in electrical connection with conductor 131 of the conveyor circuit. Signal light 161 is in electrical connection with conductor 153 and with conductor 155 when the set of contacts indicated at 163 is closed. The contacts of this set are normally open and are activated by relay coil 171 which also activates a set of contacts indicated at 173. The contacts of this set are normally closed and are in electrical connection with conductor 131 of the conveyor circuit. Coil 171 is in electrical connection with conductor 155 and with terminal 175 of device 147. Relay coil 265 is in electrical connection with conductor 155 and with conductor 153 when both the set of contacts indicated at 267 and the set of contacts indicated at 269 is closed. The set of contacts indicated at 267 is closed by the tripping of movable arm 2116 of limit switch 207 and the set of contacts indicated at 269 is closed by the tripping of movable arm 216 of limit 217. The closing of the sets of contacts indicated at 267 and 269 actuates relay coil 265 which opens the set of contacts indicated at 227 and closes the set of contacts indicated at 225. Terminals 177 and 179 of device 147 are here shown in electrical connection with conductors 181 and 183 which in turn are in electrical connection with a spring actuated pressure switch or reset button 185 as in FIGURE 2.

Referring now to FIGURE 4, conductors 153 and 155 also shown in FIGURES 2 and 3 are in electrical connection with a step-down transformer indicated generally at 311 where the potential of the current flowing from the power source mentioned in the description of FIGURES 2 and 3, e.g., 110 volts A.C., is decreased to provide a difference of potential of about 1 to 5 volts between conductors 313 and 321. Conductor 313 is in electrical connection with meter coil 315 and conductor 317. Conductor 317 is in electrical connection with conductor 434 in both FIGURES 2 and 3. Conductor 321 is in electrical connection with rectifier 323 by which alternating current is converted to a direct current, conductor 325, variable resistor 327 providing means for gross calibration of the system, conductor 329, resistor 331, conductor 333, resistor 335, conductor 337, resistor 339, conductor 341, resistor 343, conductor 345, potentiometer 347 for fine calibration of the measuring system, and conductor 349. Conductor 349 is in electrical connection with conductor when 147 is employed in the system shown in FIG- URE 2 and with conductor 245 when 147 is employed in the system shown in FIGURE 3.

Resistors 351 and 353 are in electrical connection with conductors 313 and 337 and together with the aforementioned resistors limit the flow of current to both the segmented brush rail and to meter coil 315.

Condenser 335 is in electrical connection with conductors 313 and 325 and provides means for gross stabilization of voltage in the measuring system. Constant voltage is further assured by voltage regulator tube 357 which is in electrical connection with conductors 313 and 329.

In operation terminal 177 is in electrical connection with terminal 179 through conductors 181 and 183 and reset switch 185 shown in FIGURES 2 and 3. Meter Coil 315 has associated therewith a movable arm, not shown. Sealing coil 359 is electrically connected to a set of contacts indicated at 361. The set of contacts indicated at 361 can be preset so that a predetermined resistance to closing is assured. Upon the how of a current through coil 315 above a predetermined value the set of contacts indicated at 361 is forced closed electromechanically via a movable arm associated with coil 315. The closing of this circuit actuates relay coil 363 which is in electrical connection with terminal 177 and conductor 325. The actuation of coil 363 causes a set of contacts indicated at 365 to close thereby actuating coil 171 of the control system shown in either FIGURE 2 or FIGURE 3 depending on the s3 stem in which 147 is employed.

Referring now to FIGURES 2 and 4, when articles 15 and 17, moving from right to left with respect to FIGURE 2, make electrical contact with bus bar segments 24 and 26, respectively, the electrical connection, if any, between such articles is automatically determined and the resulting flow of electrical energy therebetween, if any, is measured as being either above or below a predetermined allowable maximum.

If such connection exists, the resulting flow of electric current into coil 315 will cause the set of contacts indicated at 361 to close via an activating .arm or other appropriate device, not shown. Once closed the set of contacts indicated at 361 remains closed in this embodiment until released through manual operation of reset button 185. The closing of the set of contacts indicated at 361 in turn activates coil 363 which causes the set of contacts indicated at 365 to close thereby actuating coil 171 shown in FIGURE 2. The actuation of coil 1'71 causes the set of contacts indicated at 163 to close thereby actuating the signal indicated at 161. In this embodiment the actuation of coil 171 also causes the set of contacts indicated at 173 to open thereby breaking the conveyor run circuit and stopping the conveyor. Upon removal of the electrical connection between articles 15 and 17 the operator presses reset button switch 185. This action serves two functions in this embodiment. First, the set of contacts indicated at 361 is reopened; and, second, the break in the flow of current to coil 363 deactivates such coil. The deactivation of coil 363 in turn causes the opening of the set of contacts indicated at 365, deactivation of coil 171, the opening of the set of contacts indicated at 163, and closing of the set of contacts indicated at 173.

Reset button switch 185 is spring cont-rolled and, upon the release of pressure thereon, returns to its original position closing the electrical connection between terminals 177 and 179. Upon the actuation of the aforementioned signal at 161 and/or the stopping of the conveyor via the set of contacts indicated at 173, the operator may open the conveyor circuit via a manually operated switch, not shown, and leave this open until the electrical connection between the workpieces has been removed. Where such a switch is employed, the closing of the switch will restart the conveyor after the pressure on reset switch 185 has been released and switch 185 has returned to its normally closed position. If the electrical connection between the workpieces has been effectively removed, the conveyor will continue to run until another pair of electrically connected workpieces enters the test area. If the connection is not effectively removed, the set of contacts indicated at 361 will immediately close again repeating the warning and stopping the conveyor.

In another embodiment reset button switch 185 is eliminated and the contacts indicated at 361 are constructed and arranged such that they reopen upon the break in the flow of current therethrough caused by the removal of the electrical connection between the adjacent workpieces.

Referring now to FIGURES 3 and 4, when article 201 supported by a single hanger comes into electrical connection with segment 26 and the lead portion of article 208, which is supported by two hangers, comes into electrical connection with segment 24 and both move toward the bath, movable dogs 205 and 215 respectively contact movable arms 206 and 216 of limit switches 207 and 217 respectively. The tripping of switch 207 causes the set of contacts indicated at 267 to close. The tripping of switch 217 causes the set of contacts indicated at 269 to close. The simultaneous closing of the contacts at 267 and 269 actuates coil 265 which closes the set of contacts indicated at 225 and opens the set of contacts at 227. When the set of contacts indicated at 225 is closed and the set of contacts indicated at 227 is open, conductor 24-5 is in electrical connection with segment 24 of the bus bar. Segment 26 is in electrical connection with conductor 143. The electrical connection, if any, can then be detected by the resistance measuring apparatus in 147 as heretofore explained in relation to FIGURES 2 and 4.

Once electrical connection has been established between the proper test segments the resistance measuring, the actuation of the warning signal, and the stopping of the conveyor proceeds as aforedescribed for the previous embodiment. Movable arms 206 and 216 are spring actuated and upon being tripped spring back to their original positions when out of contact with tripping means 205 and 215. This reopens the contacts at 267 and 269, deactivates coil 269, and causes the contacts at 225 to open and the contacts at 227 to close.

As the conveyor moves on the article 208 reaches the lateral location indicated by broken outline and identified as 208A with article 218 now occupying the lateral position indicated in broken outline and identified as 218A. In this position article 208 is in electrical connection with segment 26 and article 218 is in electrical connection with segment 22. In moving toward the bath movable dog 215 contacts movable arm 206 of limit switch 207 momentarily closing the set of contacts indicated at 267. However, the movable arm 216 of limit switch 217 will not be tripped since the next approaching tripping means, movable dog 223, is still above segment 22. Thus, the set of contacts indicated at 269 will not be closed simultaneously with the set indicated at 267 and coil 265 will not be activated at this time. Hence the set of contacts indicated at 225 which is now open will remain open and the set of contacts indicated at 227 which is now closed will remain closed. Thus, conductor 245 is in electrical connection with segment 22 for this measurement and conductor 143 is still in electrical connection with segment 26. This allows the electrical connection between articles 208 and 218 to be checked via 147 as in the previous examples.

Movable dogs or tripping means such as those indicated at 205, 215 and 223 must be placed on the line in accordance with the distribution of different size workpieces either when the workpieces are attached or between this point and the test area.

In another embodiment the overall line length, i.e., the distance between the front edge of the lead object of a given pair of the rear edge of the trailing object of the pair with respect to the coating tank, or the number of connections between object and conveyor is scanned electrically and/or electronically as they pass to the tank and the current measuring device is automatically shifted in accordance with said scanning to measure the flow of electric current between each pair of objects passing through the scanning zone.

The foregoing detailed description of the embodiments shown in the drawings is submitted solely for purposes of illustration. Those skilled in the art will be aware that numerous modifications can be made in the .aforedescribed system without departing from the spirit and the scope of the invention as expressed in the claims.

We claim:

1. In a method of coating wherein electrically conductive objects separately suspended from a conveyor from which they are electrically insulated are successively passed in line through an aqueous bath having organic film-forming material dispersed therein and a first electrode in contact therewith, each of said objects while passing through said bath serving as a second electrode, and a direct electric current is provided between said first electrode and said second electrode until a substantially water insoluble coating of said material is deposited upon said second electrode, the improvement which comprises causing a first object of said line prior to entering said bath to pass through a resistance measuring zone wherein a difference of electric potential is provided between said first object and the next succeeding object in said line, measuring the resistance to the flow of electrical energy between said first object and said succeeding object while both are in movement through said zone, and utilizing said flow when it exceeds a predetermined value to signal the approach to said bath of electrically connected objects in said line.

2. In a method of coating wherein electrically conductive objects separately suspended from a conveyor from which they are electrically insulated are successively passed in line through an aqueous bath having organic film-forming material dispersed therein and a first electrode in contact therewith, each of said objects while passing through said bath serving as a second electrode, and a direct electric current is provided between said first electrode and said second electrode until a substantially water insoluble coating of said material is deposited upon said second electrode, the improvement which comprises causing a first object of said line prior to entering said bath to pass through a resistance measuring zone wherein a difference of electric potential is provided between said first object and the next succeeding object in said line, measuring the resistance to the flow of electrical energy between said first object and said succeeding object while both are in movement through said zone, and utilizing said flow when it exceeds a predetermined value to stop said conveyor.

3. In a method of coating wherein electrically conductive objects separately suspended from a conveyor from which they are electrically insulated are successively passed in line through an aqueous bath having organic film-forming material dispersed therein and a first electrode in contact therewith, each of said objects entering said bath with the polarity of said first electrode and having said polarity reversed after submergence in said bath thereby forming a second electrode, and a direct electric current is provided between said first electrode and said second electrode until a substantially water insoluble coating of said material is deposited upon said second electrode, the improvement which comprises causing a first object of said line prior to entering said bath to pass. through a, resistance measuring zone. wherein a dif- 9 ference of electric potential is provided between said first object and the next succeeding object in said line, measuring the resistance to the flow of electrical energy between said first object and said succeeding object while both are in movement through said zone, and utilizing said flow when it exceeds a predetermined value to signal the approach to said bath of electrically connected objects in said line and stop said conveyor.

4. In a method of coating wherein electrically conductive objects separately suspended from a conveyor from which they are electrically insulated are successively passed in line through an aqueous bath having organic film-forming material dispersed therein and a first electrode in contact therewith, each of said objects serving as a second electrode in said bath, a direct electric current is provided between said first electrode and said second electrode until a substantially water insoluble coating of said material is anodically deposited upon said second electrode, and the polarity of said object is reversed to that of said first electrode before said object emerges from said bath after coating, the improvement which comprises causing a first object of said line prior to entering said bath to pass through a resistance measuring zone wherein a difference of electric potential is provided between said first object and the next succeeding object in said line, measuring the resistance to the fiow of electrical energy between said first object and said succeeding object while both are in movement through said zone, and utilizing said flow when it exceeds a predetermined value to signal the approach to said bath of electrically connected objects in said line and stop the conveyor.

5. Apparatus for use in coating electrically conductive objects comprising in combination a coating tank adapted to retain an aqueous bath having organic film-forming material dispersed therein, a first electrode positioned to be in contact with said bath when said tank is charged with said bath, conveyor means for transporting a line of electrically conductive objects electrically insulated therefrom into said tank, means for providing a flow of electrical energy between said first electrode and an object of said line when both are in contact with said bath, means for providing a diiference of electric potential between each of said objects and the next succeeding object in said line prior to the entry of either into said tank, means for measuring flow of electric current between each such object and the next succeeding object of said line as the pair of objects moves to said tank, and means for utilizing said electric current when it exceeds a predetermined value to stop said conveyor.

6. Apparatus for use in coating electrically conductive objects comprising in combination an electrically conductive coating tank adapted to retain an aqueous bath having organic film-forming material dispersed therein and to serve as a first electrode, endless conveyor means for transporting a line of electrically conductive objects electrically insulated therefrom into said tank, means for providing a flow of electrical energy between an object or" said line and said tank when said object is in contact with said bath, means for providing a difference of electric potential between each of said objects and the next succeeding object in said line prior to entry of either into said tank, means for measuring flow of electric current between each such object and the next succeeding object of said line as the pair of objects moves to said tank under said difierence of potential, and means for utilizing said electric current when it exceeds a predetermined value to stop said conveyor.

7. Apparatus for use in coating electrically conductive objects of difierent size suspended from a common conveyor comprising in combination a coating tank adapted to retain an aqueous bath having organic film-forming material dispersed therein, a first electrode positioned to be in contact with said bath when said tank is charged with said bath, endless conveyor means for transporting electrically conductive objects electrically insulated therefrom into said tank, suspension means connecting each such object with said conveyor means, means for providing a flow of electrical energy between said first electrode and an object of said line when both are in contact with said bath, means for providing a difference of electric potential between each object and the next succeeding object of said line prior to entry of either into said tank, current measuring means for measuring flow of electric current between each such object and the next succeeding object of said line while the pair of objects is in move ment to said tank, said current measuring means including means adapted to distinguish objects of said line connected to said conveyor means by a lesser number of said suspension means from objects of said line connected to said conveyor means by a greater number of said suspension means and to automatically adjust said current measuring means to measure flow of electric current between each succeeding pair of objects of said line when the total number of said suspension means per pair of objects changes, and means for utilizing said electric current when it exceeds a predetermined value to stop said conveyor.

8. Apparatus for use in coating electrically conductive objects of different size suspended from a common conveyor comprising in combination an electrically conductive coating tank adapted to retain an aqueous bath having organic film-forming material dispersed therein and to serve as a first electrode, endless conveyor means for transporting electrically conductive objects electrically insulated therefrom into said tank, means for providing a flow of electrical energy between an object of said line and said tank when said object is in contact with said bath, means for providing a difference of electric potential between each object and the next succeeding object of said line prior to entry of either into said tank, current measuring means for measuring flow of electric current between each such object and the next succeeding object of said line while the pair of objects is in movement to said tank under said difference of potential, scanning means associated with said current measuring means adapted to determine the overall line length of each adjacent pair of objects and to automatically adjust said current measuring means to measure flow of electric current between each succeeding pair of objects of said line when said overall line length changes from pair to pair, and means for utilizing said electric current when it exceeds a predetermined value to stop said conveyor.

References Cited by the Examiner UNITED STATES PATENTS 3,200,057 8/1965 Burnside et al. 204-481 3,200,058 8/1965 Oster 204-181 JOHN H. MACK, Primary Examiner.

E. ZAGARELLA, Assistant Examiner. 

1. IN A METHOD OF COATING WHEREIN ELECTRICALLY CONDUCTIVE OBJECTS SEPARATELY SUSPENDED FROM A CONVEYOR FROM WHICH THEY ARE ELECTRICALLY INSULATED ARE SUCCESSIVELY PASSED IN LINE THROUGH AN AQUEOUS BATH HAVING ORGANIC FILM-FORMING MATERIAL DISPERSED THEREIN AND A FIRST ELECTRODE IN CONTACT THEREWITH, EACH OF SIAD OBJECTS WHILE PASSING THROUGH SAID BATH SERVING AS A SECOND ELECTRODE, AND A DIRECT ELECTRIC CURRENT IS PROVIDED BETWEEN SAID FIRST ELECTRODE AND SAID ELECTRODE UNTIL A SUBSTANTIALLY WATER INSOLUBLE COATING OF SAID MATERIAL IS DEPOSITED UPON SAID SECOND ELECTRODE, THE IMPROVEMENT WHICH COMPRISES CAUSING A FIRST OBJECT OF SAID LINE PRIOR TO ENTERING SAID BATH TO PASS THROUGH A RESISTANCE MEASURING ZONE WHEREIN A DIFFERENCE OF ELECTRIC POTENTIAL IS PROVIDED BETWEEN SAID FIRST OBJECT AND THE NEXT SUCCEEDING OBJECT IN SAID LINE, MEASURING THE RESISTANCE TO THE FLOW OF ELECTRICAL ENERGY BETWEEN SAID FIRST OBJECT AND SAID SUCCEEDING OBJECT WHILE BOTH ARE IN MOVEMENT THROUGH SAID ZONE, AND UTILIZING SAID FLOW WHEN IT EXCEEDS A PREDETERMINED VALUE TO SIGNAL THE APPROACH TO SAID BATH OF ELECTRICALLY CONNECTED OBJECTS IN SAID LINE. 